This invention relates generally to a fiber optic (FO) bus distribution system employed to interface a group of microprocessors distributed along the FO bus and more particularly, to such a system that includes redundant fail/safe repeaters (amplifiers) which, within certain limitations, can fail without disrupting the operation of the overall system.
In bus distributions systems employing a common FO bus with distributed subscriber processors (stations) coupled thereto by coupling logic at various positions along the FO bus, the data-representing light energy flowing in the FO bus is converted into electrical signals by a receiver portion of the coupling logic and supplied to a subscriber processor where it is processed. Conversely, the electrical signals from each subscriber processor are converted to light energy by means of a transmit portion of the coupling logic and supplied back to the FO bus as light energy.
Each processor or subscriber station and the associated coupling logic is defined as a node of the total system. To couple the light energy in either direction between the FO bus and the stations, four port star couplers are typically employed in the prior art. The four port star coupler provides a uni-directional flow of light energy through the FO bus with a portion of the energy passing through coupling logic to the subscriber processor as electrical energy. Energy is then supplied from the processor back to the coupling logic where the electrical signals are transformed into light signals and supplied into the FO bus.
In four port star couplers, however, transfer losses of approximately 3 db occur. Such losses limit the number of nodes (couplers and processors) which may be interconnected in serial manner along the FO bus, before a given processor subscriber in the system no longer receives sufficient energy to function properly. Accordingly, repeaters are typically inserted along the FO bus at appropriate intervals to compensate for the losses occurring in the star couplers and to maintain the level of transmitted light energy sufficiently high to enable the processor subscribers to function properly. Such repeaters commonly take the form of a PIN or photo avalanche diode detector (the repeater receiver) placed in the FO bus back-to-back with an LED or laser driver (the repeater transmitter), which together reconstitute the light energy.
Such an arrangement, however, has the disadvantage that failure of any single repeater will disrupt the loop and cause a system failure, resulting in loss of data. For a more complete description of such prior art, reference is made to co-pending application, Ser. No. 451,429, filed Dec. 20, 1982, by Robert F. Haworth, entitled "Repeater for Fiber Optic Distribution System", assigned to the same assignee as the present invention, and incorporated herein by reference.
The present invention provides a system incorporating fail/safe redundant repeaters which will permit the system to continue operating even after the complete failure of one of the redundant repeaters or a receiver in one of the redundant repeaters and a transmitter in the other.